The soybean aphid, Aphis glycines, can cause massive damage and over 50% yield loss to soybean crops resulting in significant agricultural losses with widespread consequences for both the food supply and other industries that rely on plant materials. Soybean cultivars currently available commercially in the United States are all susceptible to Aphis glycines to some degree, and insecticide applications are currently employed to control the disease. In addition to crop loss, increased use of insecticides to combat aphids decreases farmers' profits and may adversely affect the environment and consumer preferences. Over seven million acres of soybeans in the North Central U.S. were sprayed with insecticide to control soybean aphids in 2003 at an estimated cost of $84-$105 million (Landis et al. NCR-125 Arthropod biological control: state reports for 2003; Li et al., Mol Breeding 19:25-34, 2007).
Soybean aphids directly damage the soybean plant by removing significant amounts of water and nutrients resulting in yellow and wilted leaves. Aphids also excrete honeydew, a sugary sticky substance, on to the leaves and plants. The presence of honeydew often leads to the development of sooty mold, which adversely affects photosynthesis and results in significant yield losses (Gomez et al., Environ Exp Bot 55: 77-86 (2006)). Soybean aphids are also vectors for a number of viruses that can inhibit plant growth, distort leaves, cause mottling of leaves and stem, reduce pod number, and cause seed discoloration. Viruses transmitted via soybean aphid include, soybean mosaic virus, yellow mosaic virus, tobacco etch virus, and tobacco vein mottling virus (Wang et al. Plant Dis 90: 920-926 (2006)). As such, there is a long felt need to reduce the incidence and/or impact of aphids on crop production. Aphid resistant cultivars are needed to reduce insecticide costs and yield losses due to Aphis glycines. 
There is a need for rapid, cost-efficient method to assay the absence or presence of aphid resistance loci in soybean and there is a need for soybean plants and seeds which exhibit resistance to the soybean aphid.